U.S. patent application number 10/804277 was filed with the patent office on 2006-11-09 for titanium dioxide nanopowder manufacturing process.
Invention is credited to Charles David Musick, Austin H. JR. Reid, Lu Zhang.
Application Number | 20060251573 10/804277 |
Document ID | / |
Family ID | 34838930 |
Filed Date | 2006-11-09 |
United States Patent
Application |
20060251573 |
Kind Code |
A1 |
Musick; Charles David ; et
al. |
November 9, 2006 |
TITANIUM DIOXIDE NANOPOWDER MANUFACTURING PROCESS
Abstract
Titanium dioxide nanopowder is produced by a process,
comprising: (a) reacting titanium tetrachloride and an oxygen
containing gas in the vapor phase in a flame reactor, at a flame
temperature of at least about 800.degree. C., a pressure ranging
from about -35 to about 172 kPa (about -5 to about 25 psig) in the
presence of (i) water vapor in an amount ranging from about 1000 to
about 50,000 parts per million, based on the weight of titanium
dioxide under production, (ii) a diluent gas in an amount greater
than about 100 mole percent based on the titanium tetrachloride and
oxygen containing gas and (iii) a nucleant consisting essentially
of a cesium substance wherein the cesium substance is present in an
amount ranging from about 10 to about 5000 parts per million, based
on the weight of the titanium dioxide under production, to form
titanium dioxide nanopowder, and recovering the titanium dioxide
nanopowder having a surface area in the range of about 30 to about
300 m.sup.2/g and wherein about 50 volume percent of the particles
have a diameter of about 80 nm or less and wherein about 90 volume
percent of the particles have a diameter of about 100 nm or
less.
Inventors: |
Musick; Charles David;
(Waverly, TN) ; Reid; Austin H. JR.; (Wilmington,
DE) ; Zhang; Lu; (Newark, DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
34838930 |
Appl. No.: |
10/804277 |
Filed: |
March 19, 2004 |
Current U.S.
Class: |
423/613 |
Current CPC
Class: |
C01G 23/07 20130101;
C01P 2006/12 20130101; B82Y 30/00 20130101; Y10S 977/811 20130101;
C01P 2004/51 20130101; C01P 2004/64 20130101; Y10S 977/773
20130101; Y10S 977/775 20130101; C01P 2006/60 20130101; Y10S
977/777 20130101 |
Class at
Publication: |
423/613 |
International
Class: |
C01G 23/047 20060101
C01G023/047 |
Claims
1. A process for producing titanium dioxide nanopowder, comprising:
(a) reacting titanium tetrachloride and an oxygen containing gas in
the vapor phase in a flame reactor, at a flame temperature of at
least about 800.degree. C. in the presence of (i) water vapor in an
amount ranging from about 1000 to about 50,000 parts per million,
based on the weight of titanium dioxide under production, (ii) a
diluent gas in an amount greater than about 100 mole percent based
on the titanium tetrachloride and oxygen containing gas and (iii) a
nucleant consisting essentially of a cesium substance wherein the
cesium substance is present in an amount ranging from about 10 to
about 5000 parts per million, based on the weight of the titanium
dioxide under production, the pressure of reaction being sufficient
to form titanium dioxide nanopowder, and (b) recovering the
titanium dioxide nanopowder having a surface area in the range of
about 30 to about 300 m.sup.2/g and wherein about 50 volume percent
of the particles have a diameter of about 80 nm or less and wherein
about 90 volume percent of the particles have a diameter of about
100 nm or less.
2. The process of claim 1 in which the cesium substance is present
in an amount ranging from about 50 to about 1000 parts per
million.
3. The process of claim 1 in which the temperature is in the range
of about 800 to about 1800.degree. C.
4. (canceled)
5. The process of claim 1 in which the titanium tetrachloride and
the oxygen containing gas are reacted in a reaction zone in which
the titanium tetrachloride and the diluent are is introduced into
the reaction zone in a mixture.
6. The process of claim 1 in which the diluent is recycle gas.
7. The process of claim 1 in which the flame reactor further
comprises a means for increasing heat transfer.
8. The process of claim 1 in which the cesium substance is a cesium
halide or salt of an organic acid.
9. The process of claim 1 in which the residence time for reacting
the titanium tetrachloride and the oxygen containing gas ranges
from about 5 to about 40 milliseconds.
10. The process of claim 1 in which the titanium dioxide is
predominantly in the anatase crystalline form.
11. The process of claim 1 in which the pressure of reaction ranges
from about 0 to about 172 kPa.
12. The process of claim 1 in which the pressure of reaction ranges
from about 0 to about 138 kPa.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to the manufacture of titanium
dioxide nanopowder. More particularly, the invention relates to the
manufacture of titanium dioxide nanopowder of controlled particle
size in a gas phase flame reactor by using a cesium substance.
[0003] 2. Background of the Invention
[0004] The scientific and technological advantages of
nanostructured particles and materials have been attracting
considerable attention. The small size of nanoparticles (generally
used to indicate particles less than 100 nm in diameter), which can
be responsible for different useful properties (electronic,
optical, electrical, magnetic, chemical, and mechanical), makes
them suitable for a wide variety of industrial applications.
[0005] The manufacture of pigmentary titanium dioxide by oxidizing
titanium tetrachloride in the gas phase in a flame reactor with an
oxygen-containing gas is known. U.S. Pat. No. 5,201,949 describes
the addition of cesium chloride for purposes of improving carbon
black undertone, specific surface area and gloss properties.
[0006] Producing titanium dioxide nanopowder in a commercial scale
flame reactor poses significant challenges. Identifying the
appropriate operating conditions that can produce acceptable
nanopowder product without causing reactor pluggage can be a
significant a problem. Also operating conditions considered useful
for producing titanium dioxide nanopowder can be difficult to carry
out in a flame reactor due to aforementioned concerns with reactor
pluggage and to related operating parameters that lead to the
formation of particles and aggregates of particles of a size larger
than that desired for typical nanoparticle applications. Deliberate
control of a flame reactor in a manner that promotes the
preferential generation of nanoparticulate materials is made
difficult due to a propensity of impacts between particles at high
pressures and mass loadings, leading to aggregate formation and
particle growth. This can also lead to excessive wall deposition,
resulting in the constriction of flow and ultimately to downstream
pluggage of the reactor system.
SUMMARY OF THE INVENTION
[0007] In accordance with this invention there is provided a
process for producing titanium dioxide nanopowder, comprising:
[0008] (a) reacting titanium tetrachloride and an oxygen containing
gas in the vapor phase in a flame reactor, at a flame temperature
of at least about 800.degree. C., a pressure ranging from about -35
to about 172 kPa (about -5 to about 25 psig) in the presence of (i)
water vapor in an amount ranging from about 1000 to about 50,000
parts per million, based on the weight of titanium dioxide under
production, (ii) a diluent gas in an amount greater than about 100
mole percent based on the titanium tetrachloride and oxygen
containing gas and (iii) a nucleant consisting essentially of a
cesium substance wherein the cesium substance is present in an
amount ranging from about 10 to about 5000 parts per million, based
on the weight of the titanium dioxide under production, to form
titanium dioxide nanopowder, and recovering the titanium dioxide
nanopowder having a surface area in the range of about 30 to about
300 m.sup.2/g and wherein about 50 volume percent of the particles
have diameter of about 80 nm or less and wherein about 90 volume
percent of the particles have a diameter of about 100 nm or
less.
[0009] This invention can provide a method of making titanium
dioxide nanopowder having a controlled particle size as determined
by a particle size diameter measurement wherein about 10 volume
percent of the particles can have diameter of about 30 nm or less,
specifically about 25 nm or less, more specifically about 10 nm or
less. Further, about 50 volume percent of the particles can have a
particle size diameter of about 80 nm or less, specifically about
75 nm or less, more specifically about 50 nm or less. Still
further, about 90 volume percent of the particles can have a
particle size diameter of about 100 nm or less, specifically about
80 nm or less, more specifically about 75 nm or less. The particle
size diameter measurements are for the aggregate particles, not for
the primary particles.
[0010] The surface area of the particles can be in the range of
about 30 to about 300 m.sup.2/g, specifically about 50 to about 200
m.sup.2/gram, more specifically about 75 to about 150
m.sup.2/g.
[0011] It is contemplated that the process of this invention can
permit higher nanopowder TiO.sub.2 output while still maintaining
the controlled particle size. The materials should show strong
absorbance of ultraviolet radiation in the range of 400 nm and
below, while demonstrating very low scattering in the visible
wavelengths of 400 to 800 nm.
[0012] Typically, the carbon black undertone of the titanium
dioxide nanopowder of this invention will be above about 30,
specifically above about 40.
DETAILED DESCRIPTION OF THE INVENTION
[0013] The titanium tetrachloride and the oxygen containing gas are
reacted in the presence of a cesium substance, typically a nucleant
consisting essentially of a cesium substance. One function of the
cesium substance is to control the particle size. It was found that
the cesium substance can control the particle sizes ranges achieved
in the production of titanium dioxide nanopowder in a flame
reactor. The nucleant typically consists essentially of a cesium
substance. By nucleant it is meant any substance which can aid in
the formation of a nanopowder. By consisting essentially of it is
meant that a nucleant other than a cesium substance can be present,
provided that it is selected and is present in such an amount that
it does not negate or nullify the benefits of the cesium substance
such as particle size control. By cesium substance it is meant any
form of cesium or a mixture of various forms of cesium which can
provide titanium dioxide nanopowder including cesium metal, cesium
salt, cesium oxide and other compounds containing cesium. Any
compound of cesium with a vapor pressure suitable for the reaction
conditions or that is soluble in water can be considered. Halides,
salts of organic acids, including without limit carboxylic acids,
and salts containing polyoxoanions such as phosphate or sulfate
could be used.
[0014] If a cesium substance is used with a nucleant other than a
cesium substance, then such nucleant typically will not be present
in an amount in excess of that specified hereinafter for the cesium
substance. Preferably, such nucleant will be present in an amount
less than that of the cesium substance.
[0015] Examples of cesium substances include cesium oxide, cesium
halides (chlorides, iodides, bromides, fluorides), nitrates,
phosphates, carbonates, sulfates, acetates, alcoholates, benzoates,
hydroxides and oxides. Typically cesium salts or water solutions of
cesium salts such as cesium iodide, cesium chloride or cesium
carbonate can be used. Anions of the salt can be used. Also, the
cesium substance can be substantially volatile at the reaction
temperatures utilized for the production of the titanium dioxide
nanopowder.
[0016] Any convenient procedure for adding the nucleant of this
invention can be used and will be apparent to those skilled in the
flame reactor art. Typical procedures are described in U.S. Pat.
Nos. 3,208,866 and 5,201,949. The nucleant can be added to or
incorporated in the reactant oxygen gas stream being charged to the
reactor either as a finely divided solid, as a water solution, as a
nonaqueous solution, as a molten salt, or as a colloidal
dispersion. If desired, the nucleants can be charged directly into
the reaction zone or to the mixed or mixing reactants just ahead of
the actual flame of the reaction.
[0017] The water solutions of the soluble salts of the nucleants of
this invention can provide a means for controlling product
properties and compensating for variations in other process
conditions. For example the amount of a given salt solution used
can be varied to hold the carbon black undertone value constant. To
provide more accurate control without varying the amount of water
vapor used, two salt solutions of different concentrations can be
provided and blended as desired at constant water consumption.
These solutions are usually made up with pure agents. However, the
presence of other substances which are not deleterious can be
tolerated. Mixtures of salts can also be effective. Naturally
occurring solutions and brines which contain the nucleants and
which are free of discoloring ions may be used if clear or
clarified of silt and other debris.
[0018] The amount of the cesium substance present can be in the
range of about 10 to about 5000 parts per million, based on the
weight of the titanium dioxide under production. The cesium will
more specifically be present in an amount ranging from about 50 to
about 1000 parts per million. The amount of the cesium substance is
based on the weight of the cesium or other cesium component of the
cesium salt, cesium oxide or cesium compound used. The amount of
cesium substance can be increased for smaller particles with a
greater surface area. When producing nanopowder, the greater number
of higher surface area particles in the reactor can require large
quantities of the cesium substance; that is, greater than about 200
ppm. While a quantity of cesium substance in the production of
pigment size particles exceeding about 200 ppm can have a
detrimental impact on CBU, it is believed that large quantities of
cesium substance may not have the detrimental impact on CBU when
making nanopowders.
[0019] A third gas hereinafter referred to as a diluent can be used
in the process of this invention. The diluent gas may be introduced
into the reactor by any convenient method; such methods will be
apparent to those skilled in the flame reactor art. The diluent gas
can be added together with the titanium tetrachloride. This diluent
gas is considered to facilitate the production of small particle
sizes by inhibiting particle agglomerations. The diluent gas may
also be useful for preventing deposition of solids within the
reactor. The diluent gas can also be used as a carrier for the
nucleant. A solution of the nucleant can be sprayed into the gas
stream and conveyed into the reactor as a mist. Also they may be
conveyed as a fine solid or smoke. The diluent gas can be inert and
should not react with the reactants or the reaction product under
the conditions under which the reaction product is produced.
Examples of suitable diluent gases include chlorine, nitrogen,
carbon dioxide, noble gases (e.g. helium, neon or argon), and
recycle gas, i.e., gas withdrawn from the reactor outlet from which
the titanium dioxide is removed. Typically the recycle gas contains
chlorine, carbon dioxide nitrogen and/or oxygen. The amount of the
diluent gas can range from greater than about 100 mole percent
based on the titanium tetrachloride and oxygen reactants,
specifically about 100 to about 500. The typical mole ratio of
diluent to TiO.sub.2 is 1.5:1. However, the amount of diluent can
vary depending upon the flue diameter and the operating pressure.
Suitable methods for introducing the diluent would be apparent to
those skilled in the flame reactor art, including the method
described in U.S. Pat. No. 5,508,015.
[0020] An amount of aluminum trichloride suitable to provide the
rutile crystalline form of the titanium dioxide can be used.
Without aluminum trichloride a product containing a predominant
amount of the anatase crystalline form can be manufactured. The
aluminum trichloride can be in the vapor form in an amount ranging
from about 0.1 to about 10 percent based on the weight of the
titanium tetrachloride. A procedure for incorporating aluminum
trichloride is described in U.S. Pat. No. 3,505,091.
[0021] The pressure for carrying out the reaction can range from
about -35 to about 172 kPa (about -5 to about 25 psig),
specifically about 0 to about 138 kPa (about 0 to about 20
psig).
[0022] The residence time of the reactants in the mixing zone of
the reactor can range from about 5 to about 40 milliseconds,
specifically about 10 to about 35 milliseconds.
[0023] Mean residence time (RT) is basically a function of the
volume of the reactor (V) and the volumetric flow rate of the
reactants and may be calculated using the following equation:
RT=3D/V Wherein RT is the residence time of the reactants in the
mixing zone of the reactor in seconds, D is the diameter of the
reactor's mixing zone in feet measured at about the location where
the reactants are first brought together, and V is the velocity of
the reactants in feet per second.
[0024] The flame temperature can be at least about 800.degree. C.,
specifically from about 800.degree. to about 1800.degree. C., more
specifically from about 1200.degree. C. to about 1800.degree. C.
even more specifically from about 1300 to about 1600.degree. C.
[0025] The water vapor can be present in an amount of about 1000 to
about 50,000 parts per million, based on the weight of the titanium
dioxide under production, specifically about 10,000 to about
20,000, based on the weight of the titanium dioxide under
production. Any water utilized as a solvent for the nucleant is
considered in the total amount of water added. Any
hydrogen-containing organic compound used as a liquid medium, such
as benzene, or methane burns to form water and also acts as the
water of nucleation.
[0026] The carbon black undertones ("CBU") values mentioned herein
are described in U.S. Pat. No. 2,488,440 using a rating or value of
10 rather than 100. A CBU value for titanium dioxide nanopowder
will be above about 30, specifically above about 40.
[0027] It is contemplated that the cesium substance of this
invention will have many advantages in the production of titanium
dioxide nanopowder. The addition of metal salts of Cs can increase
the number concentration of particles produced in the flame and
decrease the particle size.
[0028] It is contemplated that the process of this invention is
capable of increasing titanium dioxide nanopowder output while
still maintaining the targeted or desired level of CBU. For
example, to maximize output, a chloride process titanium dioxide
plant suitable for producing pigment-size titanium dioxide
(typically greater than 100 nm in diameter), is typically operated
with the use of KCl, and the output is increased until the CBU
falls to the desired level. (note that there usually is an inverse
relationship between titanium dioxide output and CBU, at least for
pigment-size product.) At such point, output is maximized, and
additional increases in output generally are not possible unless
CBU is decreased or expensive new equipment is installed. However,
at such point, it is contemplated that use of the cesium substance
of this invention can permit increased nanopowder product output
while still maintaining the desired level of CBU. That is, if the
cesium substance of this invention were added at such point, the
CBU would increase and the output could then be increased until the
CBU decreased to the desired level. It should be noted that such
increase in output is highly commercially significant because (1)
it is obtained without expensive capital investment, or equipment
installations or modifications, and (2) modern chlorine process
titanium dioxide plants operate at high rates (i.e. five or more
tons per hour) in production of pigment-size titanium dioxide which
rates would be beneficial for the production of nanopowder and thus
even minor percentage increases in output can result in
substantially increased pounds of output.
[0029] In a manner similar to that described in the immediately
preceding paragraph, it is believed that the process of this
invention can increase nanopowder titanium dioxide output while
still maintaining the target or desired level of gloss. Also while
certain process conditions can increase titanium dioxide gloss,
they generally decrease CBU. Under such process conditions, the use
of this invention is believed to be beneficial to increase CBU.
[0030] It is believed that the process of this invention can also
extend the times between maintenance shutdowns and/or provide
operating flexibility for chloride titanium dioxide plants. For
example, operation for extended periods of time can increase
buildup of reactants, products and by-products in the process
equipment which can increase operating pressure. Also, desired
reaction conditions may sometimes require or cause increased
pressure. The increased pressure can be a problem by causing an
adverse impact on titanium dioxide CBU, surface area and gloss
which can require (1) the output to be decreased to restore such
properties, or (2) a plant shutdown to remedy the causes of the
pressure increase. It is believed that under such conditions of
increased pressure, use of the cesium substance of this invention
could remedy some or all of such problems and thereby extend the
times between maintenance shutdowns and/or provide for greater
operating flexibility.
[0031] It is contemplated that the flame reactor of this invention
will comprise a means for increasing heat transfer. Suitable means
include without limitation finned flue equipment of the kind
described in U.S. Pat. No. 4,937,064. The use of flue piping
containing internal fins, as disclosed in the aforementioned
patent, provides a means of increasing effective heat transfer
without substantially changing the fundamental geometry of the
reaction system. Since heat removal and the control of same is
important for manufacture of particulate materials of controlled
and commercially-valuable size distribution, the finned flue
equipment can provide increased production rates and product
performance from the flame reactor system.
[0032] Fuel for the flame reactor can be any combustible gas such
as carbon monoxide, benzene, naphthalene, acetylene, anthracene
and/or methane.
[0033] In one embodiment, the invention herein can be construed as
excluding any element or process step that does not materially
affect the basic and novel characteristics of the composition or
process. Additionally, the invention can be construed as excluding
any element or process step not specified herein.
[0034] The following examples illustrate the invention.
EXAMPLES
Test Procedures Used in Examples
Surface Area
[0035] The specific surface area of a sample made according to the
Examples is defined as the surface area of one gram of particles.
It is defined by the formula: S = 6 ( Dia ) .times. ( Den )
##EQU1## wherein S is the specific surface area in square meters
per gram, Dia is the average particle diameter in meters; and Den
is the density of the pigment in grams per cubic meters.
[0036] The surface area can be determined by gas absorption or by
determining the average particle size by use of an electron
microscope and then using such particle size to calculate the
surface area by use of the above formula. Additional information
regarding determining the specific surface area is set forth in T.
P. Patton Paint Flow and Pigment Dispersion, 1979, John Wiley and
Son, Inc.
UPA Particle Size Distribution
[0037] The particle size distribution of the particles formed in
the Examples, and shown in Table 1, were measured using the
ultrafine particle analyzer dynamic light scattering technique. The
MICROTRAC ULTRAFINE PARTICLE ANALYZER (UPA) (a trademark of Leeds
and Northrup, North Wales, Pa.) uses the principle of dynamic light
scattering to measure the particle size distribution of particles
in liquid suspension. The measured size range is 0.0031 .mu.m to 6
.mu.m (3 nm to 6000 nm). The dry particle sample needs to be
prepared into a liquid dispersion to carry out the measurement. An
example procedure is as follow:
[0038] (1) Weigh out 0.08 g dry powder.
[0039] (2) Add 79.92 g 0.1% tetrasodium pyrophosphate (TSPP)
solution in water to make a 0.1 wt. % suspension.
[0040] As described in the following Examples, the gas phase
process and operating conditions of the present invention employed
in a laboratory scale flame reactor operating at a rate of 0.04
g/min of TiO2 in which the titanium dioxide nanopowder is produced
is considered to provide design data for large scale
production.
EXAMPLES
Example 1
[0041] A coflow-diffusion burner was used for aerosol synthesis of
titania nanoparticles. The reactor consists of three concentric
tubes with inner diameters of 3/16 in (4.76 mm), 3/8 in (9.52 mm)
and 9/16 in (14.29 mm) and a wall thickness of 0.035 in (0.889 mm).
TiCl.sub.4 vapor was thoroughly premixed with O.sub.2 by bubbling
O.sub.2 at a rate of 1 l/min through a cylinder maintained at room
temperature that contains liquid TiCl.sub.4. This TiCl.sub.4
containing O.sub.2 stream was introduced through the center tube.
Methane flew through the inner annulus at a rate of 0.5 l/min.
Oxygen was introduced as a carrier gas to a Baxter Healthcare
atomizer (Airlife.TM. Misty-Neb.TM. Nebulizer, Cat. 002033) at a
rate of 3 l/min. The atomizer contained CsCl aqueous solution (0.5%
by weight). This oxygen stream carrying CsCl solution droplets was
introduced into the reactor through the second annular. This
resulted in a simple diffusion flame. The flame temperature was
about 1500.degree. C., measured one cm away from the surface of the
concentric tubes. The reaction was carried out under atmospheric
pressure. All gases were delivered from cylinders with the flow
rates controlled by mass flow controllers. TiO.sub.2 particles were
formed in the flame as the product of TiCl.sub.4 oxidation and
samples were collected on a sintered metal filter. The particle
size distribution and surface area of the particles was measured
and reported in Table 1.
Example 2
[0042] The same procedure as Example 1 was followed. The particle
size distribution was measured and reported in Table 1.
Comparative Example A
[0043] In this Example, CsCl was not used.
[0044] The coflow-diffusion burner and operating conditions
described in Example 1 was used. TiCl.sub.4 vapor was thoroughly
premixed with O.sub.2 by bubbling O.sub.2 at a rate of 1 l/min
through a cylinder maintained at room temperature that contained
liquid TiCl.sub.4. This TiCl.sub.4 containing O.sub.2 stream was
introduced through the center tube. Methane flew through the inner
annulus at a rate of 0.5 l/min. Additional oxygen was provided
through the outer annulus at 3 l/min. This resulted in a simple
diffusion flame. All gases were delivered from cylinders with the
flow rates controlled by mass flow controllers. TiO.sub.2 particles
were formed in the flame as the product of TiCl.sub.4 oxidation and
samples were collected on a sintered metal filter. The particle
size distribution and surface area were measured and reported in
Table 1.
Comparative Example B
[0045] The procedure of Example 1 was followed except CsCl was not
used.
[0046] TiCl.sub.4 vapor was thoroughly premixed with O.sub.2 by
bubbling O.sub.2 at a rate of 1 l/min through a cylinder maintained
at room temperature that contained liquid TiCl.sub.4. This
TiCl.sub.4 containing O.sub.2 stream was introduced through the
center tube. Methane flew through the inner annulus at a rate of
0.5 l/min. Oxygen was introduced as a carrier gas to a Baxter
Healthcare atomizer (Airlife.TM. Misty-Neb.TM. Nebulizer, Cat.
002033) at a rate of 3 l/min. Deionized water was the liquid being
atomized. This oxygen stream carrying water droplets was introduced
into the reactor through the second annulus. This resulted in a
simple diffusion flame. All gases were delivered from cylinders
with the flow rates controlled by mass flow controllers. TiO.sub.2
particles were formed in the flame as the product of TiCl.sub.4
oxidation and samples were collected on a sintered metal filter.
The particle size distribution and surface area were measured and
reported in Table 1. TABLE-US-00001 TABLE 1 Comparative Comparative
Example 1 Example 2 Example A Example B d10 (nm) 45.8 44.7 92.7
74.7 d50 (nm) 72.4 78.1 166.5 154.3 d90 (nm) 111.2 129.8 284.5
253.1 Surface Area 61.69 not meas. 27.73 75.5
[0047] Particles made in accordance with Examples 1 and 2 in which
CsCl was added to the flame reactor had a significantly smaller
size as illustrated by the particle size distribution data reported
in Table 1. The particles made following the procedure of Example 1
also had a large surface area which is typical of small particles.
The measured surface area for the particles of Comparative Example
B was higher than expected for large particles but is considered to
have resulted from a high degree of agglomeration.
[0048] The description of illustrative and preferred embodiments of
the present invention is not intended to limit the scope of the
invention. Various modifications, alternative constructions and
equivalents may be employed without departing from the true spirit
and scope of the appended claims.
* * * * *